The present invention relates to an improvement in a roller bearing which forms a drive device or an axle used in a railroad vehicle, a differential gear used in a car, or a rotary support part used in machinery. A roller bearing according to a first aspect of the invention can be applied to all of small- and medium-sized roller bearings having an inside diameter of the order of 20-200 mm. And, a roller bearing according to a second aspect of the invention can be applied to tapered roller bearings of all sizes. Especially, in a roller bearing according to the invention, when the quantity of lubricating oil existing in the rotary support part incorporating the present roller bearing therein is small, or when the lubricating oil has dried up in a short time, the present roller bearing can be prevented against seizure or scuffing; and, further, in case where a lubricating device is out of order, the present roller bearing can be prevented against quick seizure.
Conventionally, a roller bearing is assembled in a rotary support part disposed in various machines and, as a roller bearing for forming a rotary support part to which a large load is applied, there is used a roller bearing which employs a roller (for example, a cylindrical roller, a tapered roller, or a spherical roller) as a rolling body. FIGS. 1 to 3 show, as an example of such roller bearing, a tapered roller bearing 1 to be assembled into a rotary support part to which large radial load and axial load can be applied. This tapered roller bearing 1 is composed of an outer ring 3 having a conical-concave-surface-shaped outer ring raceway 2 formed on the inner peripheral surface thereof, an inner ring 5 having a conical-convex-surface-shaped inner ring raceway 4 formed on the outer peripheral surface thereof, and a plurality of tapered rollers 6, 6 slidably interposed between the outer ring raceway 2 and inner ring raceway 4. Also, each of the tapered rollers 6, 6 has an outer peripheral surface formed as a conical-convex-surface-shaped rolling surface 7 which can be contacted with the outer ring raceway 2 and inner ring raceway 4. Further, of the outer peripheral surface two end portions of the inner ring 5, in the large-diameter-side end portion, there is formed a large-diameter-side flange portion 8 and, in the small-diameter-side end portion, there is formed a small-diameter-side flange by portion 9.
When the above-structured tapered roller bearing 1 is in operation, the tapered rollers 6, 6, as shown in FIG. 2, each rotate about their own axes as well as rotate along the outer ring raceway 2 and inner ring raceway 4 in such a manner that they are present nearer to the large-diameter sides of the outer ring raceway 2 and inner ring raceway 4, thereby allowing the outer ring 3 and inner ring 5 to rotate with respect to each other. When the above-structured tapered roller bearing 1 is in operation, the head portions 10 of the tapered rollers 6, that is, the large-diameter-side end faces of the tapered rollers 6 and the inner surface 11 of the large-diameter-side flange portion 8, as can be seen clearly from the Hertz"" elastic contact theory, are contacted with each other in such a contact ellipse 12 portion as shown by oblique lattices in FIG. 3. Since the contact state between the head portion 10 and inner surface 11 is a rolling contact with slippage, this is a severe condition from the viewpoint of friction control. Therefore, in case where the quantity of lubricating oil supplied to the tapered roller bearing 1 is excessively small or dries up, in a terrible case, there is a possibility that there can occur damage such as seizure in the tapered roller bearing 1. By the way, damage such as seizure can occur in various portions of various roller bearings including the tapered roller bearing 1 and, of these portions, the portion where the condition is the severest and damage is easy to occur is the contact portion between the head portion 10 of the tapered roller 6 and the inner surface 11 of the large-diameter-side flange portion 8. The present invention aims at preventing the contact portion from being damaged. Accordingly, the term xe2x80x9cseizurexe2x80x9d used in the present specification means seizure in the contact portion between the head portion 10 and inner surface 11.
In order to prevent the above seizure from occurring, there are conventionally known the following techniques (1)-(7).
That is:
(1) As, disclosed in JP-A-7-91452, JP-A-7-103243 and JP-A-10-110733 as well as in the Japanese Patent No. 2508178, the head portion of the tapered roller and the inner surface of the large-diameter-side flange portion are enhanced in roughness or are plateau worked into shapes in which the lubricating oil can be retained easily.
(2) Extreme-pressure additive for enhancing seizure resistance and wear resistance is added to the lubricating oil.
(3) As disclosed in JP-A-9-177774, JP-A-9-287616, JP-A-11-132242 and JP-A-7-8628U, on the head portion of the tapered roller and the inner surface of the large-diameter-side flange portion, there are formed chemically reformed films or ceramic films.
(4) As disclosed in JPA-7-259864, JP-A-8-135664, JP-A-8-135666, JP-A-9-32859, JP-A-10-47360, and JPA-11-141557, in the interior portion of the roller bearing or in the peripheral portion of the roller bearing, there is disposed an oil basin for storing lubricating oil temporarily or a reservoir for storing grease; and, when the lubricating condition is worsened, the lubricating oil or grease is supplied from the oil basin or reservoir to thereby prevent the roller bearing from seizing.
(5) As disclosed in JP-A-4-331813, JP-A-7-12133 and JP-A-10-196660 as well as in the registered utility model No. 2584623, the edge of the connecting portion between the end face and chamfered portion of the roller is rounded, whereby, even in case where the roller is skewed and the contact ellipse is in part pressed out into the chamfered portion, an edge load occurring in the contact portion can be relieved.
(6) As disclosed in JP-A-6-63932U and in the registered utility model No. 2538263, the roller bearing is formed as a sealed structure, whereby a lubricant charged once into the interior portion of the roller bearing can be prevented from flowing out therefrom.
(7) As disclosed in JP-A-9-196068 and JP-A-9-236131, by modifying the shape of the end portion of the roller, the contact point height between the end face of the roller and inner surface of the flange portion (the diameter-direction distance from the rolling surface of the roller) is made zero, thereby preventing slippage at the contact point thereof.
Of the conventional seizure preventive techniques respectively described in the above-mentioned articles (1) to (7), the five techniques (1), (3), (4), (6) and (7) respectively relate to a specially specified roller bearing but cannot be applied to an ordinary roller bearing, or, even in case where they can be applied to the ordinary roller bearing, most of them increase the cost of production. Some of the techniques shown in the article (3) can produce the roller bearing at a relatively low cost but the durability and recycling capacity of a film obtained by these techniques are not satisfactory; that is, the film can provide moderate initial performance but, due to its change with the passage of time (such as deterioration or wear), the film fails to provide its expected performance.
Also, of the remaining techniques set forth in the articles (2) and (5), the technique in the article (2) is a measure obtained by changing the property of the lubricant; that is, it has a certain degree of effect but is not an improvement in the roller bearing itself. Therefore, in order to attain seizure prevention of a higher order, it is desired that the present technique should be used in combination with an improvement in the roller bearing itself.
Further, the technique set forth in the article (5) can provide a high seizure preventive effect but increases the production cost of the roller bearing. Therefore, in order to spread its usable range, it is desired to realize a new technique which can provide a similar seizure preventive effect at a lower cost.
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional techniques. Accordingly, it is an object of the invention to provide an improved roller bearing which has sufficient seizure resistance by optimizing the internal dimensions thereof without adding specific treatments, specific shapes, or specific functions thereto.
Of the roller bearings according to the invention, the roller bearing according to a first aspect of the invention, similarly to the above-mentioned roller bearings (including a cylindrical roller bearing, a needle bearing, a tapered roller bearing, and a self-aligning roller bearing), comprises an outer ring having an outer ring raceway formed on the inner peripheral surface thereof an inner ring having an inner ring raceway formed on the outer peripheral surface thereof, and a plurality of rollers each having an outer peripheral surface serving as a rolling surface contactable with the outer ring raceway and inner ring raceway and also an axial-direction end face serving as a sliding contact surface slidingly contactable with the inner surface of a flange portion formed on at least one of the end portion inner peripheral surface of the outer ring and the end portion outer peripheral surface of the inner ring.
Especially, in the roller bearing according to the first aspect of the invention, where an axial-direction difference between the top and bottom portions of the circumferential-direction undulation of the inner surface of the flange portion is defined as axial deflection xcex4, a composite roughness ("sgr"12+"sgr"22)1/2 consisting of the root-mean-square roughness "sgr"1 of the sliding contact surface and the root-mean-square roughness "sgr"2 of the inner surface of the flange portion is defined as a flange/roller composite roughness "sgr", the flange/roller composite roughness "sgr" and axial deflection xcex4 can satisfy at least one of the following conditions (1), (2) and (3):
xcex4xe2x89xa68 xcexcm and "sgr"xe2x89xa60.22 xcexcmRMS;xe2x80x83xe2x80x83(1)
xcex4xe2x89xa612 xcexcm and "sgr"xe2x89xa60.18 xcexcmRMS;xe2x80x83xe2x80x83(2)
xe2x80x83xcex4xe2x89xa616 xcexcm and "sgr"xe2x89xa60.13 xcexcmRMS.xe2x80x83xe2x80x83(3)
Preferably, the flange/roller composite roughness "sgr" and axial deflection xcex4 may satisfy a condition (4),
xcex4xe2x89xa68 xcexcm and "sgr"xe2x89xa60.16 xcexcmRMS.xe2x80x83xe2x80x83(4)
More preferably, the flange/roller composite roughness "sgr" and said axial deflection xcex4 may satisfy a condition (5),
xcex4xe2x89xa64 xcexcm and "sgr"xe2x89xa60.16 xcexcmRMS.xe2x80x83xe2x80x83(5)
On the other hand, the roller bearing according to a second aspect of the invention, similarly to the above-mentioned conventional roller bearing (tapered roller bearing), comprises an outer ring having a conical-concave-surface-shaped outer ring raceway formed on the inner peripheral surface thereof, an inner ring having a conical-convex-surface-shaped inner ring raceway formed on the outer peripheral surface thereof, and a plurality of tapered rollers each having an outer peripheral surface serving as a conical-convex-surface-shaped rolling surface contactable with the outer ring raceway and inner ring raceway and also an axial-direction end face serving as a sliding contact surface slidingly contacted with the inner surface of a flange portion formed on at least one of the end portion inner peripheral surface of the outer ring and the end portion outer peripheral surface of the inner ring.
Especially, in the tapered roller bearing according to the second aspect of the invention, where an axial-direction difference between the top and bottom portions of the circumferential-direction undulation of the inner surface of the flange portion is defined as axial deflection xcex4, a composite roughness ("sgr"12+"sgr"22)1/2 consisting of the root-mean-square roughness "sgr"1 of the sliding contact surface and the root-mean-square roughness "sgr"2 of the inner surface of the flange portion is defined as a flange/roller composite roughness "sgr", dm using mm as the unit thereof expresses the pitch circle diameter of the tapered roller bearing, xcex2 expresses 1/2 of the cone angle of each of the tapered rollers, L using mm as its unit expresses the axial-direction length of each of the tapered rollers, and xcex8f expresses the flange angle, that is, the inclination angle of the inner surface of the flange portion with respect to a virtual plane crossing at right angles to the center axes of the outer and inner rings, the flange/roller composite roughness "sgr" and axial deflection xcex4 can satisfy at least one of the following conditions (a), (b) and (c):                               δ          ≦                                                    {                                                      0.21                    ·                                          (                                              dm                                                                              tan                            ⁡                                                          (                                                              2                                ⁢                                β                                                            )                                                                                ·                          L                                                                    )                                                        +                  0.96                                }                            /              cos                        ⁢                          xe2x80x83                        ⁢            θ            ⁢                          xe2x80x83                        ⁢            f                          ,        and                            (        a        )                                          σ          ≦                      0.22            xc3x97                          (                                                3                  xc3x97                                      10                                          -                      6                                                        ⁢                                      xe2x80x83                                    ⁢                                      dm                    2                                                  +                                  0.0044                  ⁢                                      xe2x80x83                                    ⁢                  dm                                +                0.53                            )                        ⁢                          xe2x80x83                        ⁢            μ            ⁢                          xe2x80x83                        ⁢            mRMS                          ;                            xe2x80x83                                          δ          ≦                                                    {                                                      0.36                    ·                                          (                                              dm                                                                              tan                            ⁡                                                          (                                                              2                                ⁢                                β                                                            )                                                                                ·                          L                                                                    )                                                        +                  1.28                                }                            /              cos                        ⁢                          xe2x80x83                        ⁢            θ            ⁢                          xe2x80x83                        ⁢            f                          ,        and                            (        b        )                                          σ          ≦                      0.18            xc3x97                          (                                                3                  xc3x97                                      10                                          -                      6                                                        ⁢                                      xe2x80x83                                    ⁢                                      dm                    2                                                  +                                  0.0044                  ⁢                                      xe2x80x83                                    ⁢                  dm                                +                0.53                            )                        ⁢                          xe2x80x83                        ⁢            μ            ⁢                          xe2x80x83                        ⁢            mRMS                          ;                            xe2x80x83                                          δ          ≦                                                    {                                                      0.51                    ·                                          (                                              dm                                                                              tan                            ⁡                                                          (                                                              2                                ⁢                                β                                                            )                                                                                ·                          L                                                                    )                                                        +                  1.68                                }                            /              cos                        ⁢                          xe2x80x83                        ⁢            θ            ⁢                          xe2x80x83                        ⁢            f                          ,        and                            (        c        )                                σ        ≦                  0.13          xc3x97                      (                                          3                xc3x97                                  10                                      -                    6                                                  ⁢                                  xe2x80x83                                ⁢                                  dm                  2                                            +                              0.0044                ⁢                                  xe2x80x83                                ⁢                dm                            +              0.53                        )                    ⁢          μ          ⁢                      xe2x80x83                    ⁢                      mRMS            .                                              xe2x80x83            
Preferably, the flange/roller composite roughness "sgr" and axial deflection xcex4 may satisfy the following condition (d).                               δ          ≦                                                    {                                                      0.21                    ·                                          (                                              dm                                                                              tan                            ⁡                                                          (                                                              2                                ⁢                                β                                                            )                                                                                ·                          L                                                                    )                                                        +                  0.96                                }                            /              cos                        ⁢                          xe2x80x83                        ⁢            θ            ⁢                          xe2x80x83                        ⁢            f                          ,        and                            (        d        )                                σ        ≦                  0.16          xc3x97                      (                                          3                xc3x97                                  10                                      -                    6                                                  ⁢                                  xe2x80x83                                ⁢                                  dm                  2                                            +                              0.0044                ⁢                                  xe2x80x83                                ⁢                dm                            +              0.53                        )                    ⁢          μ          ⁢                      xe2x80x83                    ⁢                      mRMS            .                                              xe2x80x83            
More preferably, the flange/roller composite roughness "sgr" and axial deflection xcex4 may satisfy the following condition (e).                               δ          ≦                                                    {                                                      0.072                    ·                                          (                                              dm                                                                              tan                            ⁡                                                          (                                                              2                                ⁢                                β                                                            )                                                                                ·                          L                                                                    )                                                        +                  0.18                                }                            /              cos                        ⁢                          xe2x80x83                        ⁢            θ            ⁢                          xe2x80x83                        ⁢            f                          ,        and                            (        e        )                                σ        ≦                  0.16          xc3x97                      (                                          3                xc3x97                                  10                                      -                    6                                                  ⁢                                  xe2x80x83                                ⁢                                  dm                  2                                            +                              0.0044                ⁢                                  xe2x80x83                                ⁢                dm                            +              0.53                        )                    ⁢          μ          ⁢                      xe2x80x83                    ⁢                      mRMS            .                                              xe2x80x83            
Next, of the above conditions for specifying the respective aspects of the invention, the concept of the axial deflection xcex4 will be described below with reference to FIGS. 4 and 5. By the way, the following description will be given with respect to a tapered roller bearing in which the effects of the invention can be obtained most clearly. The first aspect of the invention is not limited to a tapered roller bearing but can be applied to all kinds of roller bearings, provided that they include a flange portion in one of outer ring and inner ring raceways; that is, the first aspect can be applied to a cylindrical roller bearing (including a needle bearing) and a self-aligning roller bearing as well. On the other hand, the second aspect of the invention can be applied to a tapered roller bearing only.
The inner surface 11 of the large-diameter-side flange portion 8 formed on the large-diameter-side end portion of the outer peripheral surface of the inner ring forming such a tapered roller bearing as shown in the above-mentioned FIGS. 1 and 2 is formed as a partially conical-concave-surface-shaped surface. When working such inner surface 11, the center Xxcex1 of the partially conical-concave-surface-shaped surface and the center Xxcex2 of the inner ring 5 are to be matched to each other. However, in some cases, the inner surface 11 is worked in such a manner that the two centers, as shown exaggeratedly in FIG. 5, are shifted from each other by an amount equivalent to a reference mark x shown in FIG. 5 due to their inevitable manufacturing errors. In case where the center Xxcex1 of the inner surface 11 and the center Xxcex2 of the inner ring 5 are not matched to each other, the inner surface 11 is undulated in shape in the circumferential direction thereof. In other words, the axial-direction (in FIG. 5, right-and-left direction) positions of the contact portion of the inner surface 11 with the head portion 10 of the tapered roller 6 are not constant in the circumferential direction thereof, so that the top and bottom portions of the undulation are shifted from each other by a difference 8 shown in FIG. 5. This difference xcex4 is defined as the above-mentioned axial deflection. By the way, such axial deflection xcex4 can occur not only when, as shown in FIG. 5, the two centers Xxcex1 and Xxcex2 are shifted from each other while they are parallel, but also when the two centers Xxcex1 and Xxcex2 are not parallel, or when there are originally found undulations in the inner surface 11. In any case, a difference between the axial-direction positions of the top and bottom portions of the contact portion of the inner surface 11 with the head portion 10 of the tapered roller 6 provides the axial deflection xcex4.
By the way, the measurement of the axial deflection xcex4 is carried out in the following manner. That is, firstly, the inner ring 5 is placed on the upper surface of a turntable of a roundness measuring device with the large-diameter-side flange portion 8 located in the bottom. And, the inner ring raceway 4 is centered so that a shift distance between the rotation center of the turntable and the center of the inner ring 5 becomes smallest. In this state, a probe of the roundness measuring device is contacted with the contact portion of the inner surface 11 of the large-diameter-side flange portion 8 with the head portion 10 of the tapered roller 6, and the turntable is rotated, thereby measuring the undulation of the inner surface 11. And, a difference between the largest and smallest ones of the measured values is defined as the axial deflection xcex4.
In the case of the above-structured roller bearing according to the invention, not only an increase in the manufacturing cost thereof can be minimized but also, even when it operates under the poor lubricating condition, damage such as scuffing or seizure is hard to occur. That is, as the axial deflection xcex4 and the composite roughness "sgr" relating to the sliding contact surface of the roller and the inner surface of the flange portion respectively decrease in value, the above-mentioned damage can be prevented more effectively. However, in case where enhancement in the damage preventive effect is to be expected by controlling selectively only one of the axial deflection xcex4 and the composite roughness "sgr", down to a low value, high working accuracy must be realized in the selected one of the axial deflection xcex4 and the composite roughness "sgr", which increases the manufacturing cost of the roller bearing. On the other hand, since every one of roller bearings according to the invention can enhance the damage preventive effect due to the synergistic effect of the axial deflection xcex4 and the composite roughness "sgr", the working accuracy of each of the axial deflection xcex4 and the composite roughness "sgr" need not be set high. Thanks to this, as described above, while controlling an increase in the manufacturing cost, the damage preventive effect can be enhanced.
Next, description will be given below of the reason why the damage preventive effect can be obtained by controlling both of the axial deflection xcex4 and the composite roughness "sgr" down to small values.
That is, firstly, to control the axial deflection xcex4 down to a small value is effective in that it can lower the maximum value of variations in the contact surface pressures of the respective contact portions between the inner surface 11 of the large-diameter-side flange portion 8 and the head portions 10 of the respective tapered rollers 6. In other words, in the case of an ideal inner ring 5 in which the above axial deflection xcex4 is not present all (xcex4=0), the contact portions between the head portions 10 of the plurality of tapered rollers 6 and the inner surface 11 of the large-diameter-side flange portion 8 support equally the axial load applied into between the outer ring 3 and inner ring 5. Therefore, the contact surface pressures cannot be excessively large in any of the contact portions. Here, the seizure resistance can be enhanced as the product of the contact surface pressure P of the contact portion and the sliding speed V. Thus, as the PV value and calorific value become smaller, the seizure resistance enhances. Accordingly, by minimizing the maximum value of the variations in the contact surface pressures in the above-mentioned manner, the seizure resistance can be enhanced. On the other hand, in case where the axial deflection xcex4 is large, that is, a large undulation is present on the inner surface 11, the contact portions between the head portions 10 of the plurality of tapered rollers 6 and the inner surface 11 of the large-diameter-side flange portion 8 do not support equally the axial load applied into between the outer ring 3 and inner ring 5, but the contact surface pressure on the top portion of this large undulation becomes higher than the contact surface pressure on the bottom portion thereof. Due to this, the PV values become higher locally and thus the calorific values become larger, with the result that seizure is easy to occur in these portions and the seizure resistance of the bearing is thereby lowered.
Also, referring to the composite roughness "sgr", in case where a proper oil film is formed in the contact portion between the inner surface 11 of the large-diameter-side flange portion 8 and the head portion 10 of the tapered roller 6, metals can be prevented against direct contact with each other in the contact portion to thereby prevent occurrence of so called metal contact; that is, to control the composite roughness "sgr" down to a low value is effective in that the metal contact can be prevented. For example, in case where the value of the composite roughness "sgr" is large, that is, in case where the surface roughness of the inner surface 11 and/or head portion 10 is large (rough), the top portions of minute undulations existing on the surface of one metal are easy to touch the surface of the other metal directly not through the oil film. In this state, friction acting on the contact portion becomes large, which lowers the seizure resistance of the bearing.
As described above, in all of the roller bearings according to the invention, since the seizure resistance thereof is enhanced by controlling the axial deflection xcex4 and composite roughness "sgr" down to small values, even in case where the quantity of the lubricating oil to be taken into the contact portion between the inner surface 11 and head portion 10 is small, damage such as scuffing or seizure can be prevented. Also, because a sufficient seizure resisting property can be obtained even without reducing the respective values of the axial deflection xcex4 and composite roughness "sgr" down to extremely small values, it is possible to minimize an increase in the manufacturing cost of the roller bearing which is caused by enhancing the seizure resisting property of the roller bearing.